Serine-129 phosphorylation of α-synuclein is a trigger for physiologic protein-protein interactions and synaptic function

Abstract

Phosphorylation of α-synuclein at the Serine-129 site (α-syn Ser129P) is an established pathologic hallmark of synucleinopathies, and also a therapeutic target. In physiologic states, only a small fraction of total α-syn is phosphorylated at this site, and consequently, almost all studies to date have focused on putative pathologic roles of this post-translational modification. We noticed that unlike native (total) α-syn that is widely expressed throughout the brain, the overall pattern of α-syn Ser129P is restricted, suggesting intrinsic regulation and putative physiologic roles. Surprisingly, preventing phosphorylation at the Ser-129 site blocked the ability of α-syn to attenuate activity-dependent synaptic vesicle (SV) recycling; widely thought to reflect its normal function. Exploring mechanisms, we found that neuronal activity augments α-syn Ser-129P, and this phosphorylation is required for α-syn binding to VAMP2 and synapsin - two functional binding-partners that are necessary for α-syn function. AlphaFold2-driven modeling suggests a scenario where Ser129P induces conformational changes in the C-terminus that stabilizes this region and facilitates protein-protein interactions. Our experiments indicate that the pathology-associated Ser129P is an unexpected physiologic trigger of α-syn function, which has broad implications for pathophysiology and drug-development.

Spinal cord perfusion impairments in the M83 mouse model of Parkinson’s disease

“…pS129 α-syn has been the focus in understanding α-synucleinopathies because it is one of the most robust pathological markers of early α-syn aggregation, with almost all the aggregates containing this posttranslational modification (Anderson et al 2006; Fujiwara et al 2002). On the other hand, pS129 α-syn is known to play a physiological role at the synaptic level in healthy brains and it triggers protein-protein interactions(Parra-Rivas et al 2023; Ramalingam et al 2023). Accumulation of pS129 α-syn has also been observed in the context of oxygen intake and utilization disorders in cells, as well as in middle cerebral artery occlusion rodent models,(Kim et al 2016; Unal-Cevik et al 2011) and in patients with obstructive sleep apnea syndrome (Chen et al 2014).…”

“…Phospho-α-syn (p-α-syn) at Ser129 site (pS129-α-syn) exists at a low level in the healthy brain and plays a physiological role at synapses (Parra-Rivas et al 2023; Ramalingam et al 2023). Nevertheless, Ser129 site is implicated in all pathologic α-syn aggregates, making this post-translational modification an established pathological marker of α-synucleinopathy (Anderson et al 2006; Fujiwara et al 2002).…”

“…Phospho-α-syn (p-α-syn) at Ser129 site (pS129-α-syn) exists at a low level in the healthy brain and plays a physiological role at synapses (Parra-Rivas et al 2023;Ramalingam et al 2023).…”

Viral overexpression of human alpha-synuclein in mouse substantia nigra dopamine neurons results in hyperdopaminergia but no neurodegeneration

“…Phosphorylation of α-synuclein at serine-129 is considered a pathological hallmark of synucleinopathies [3,10] but has more recently been shown to also facilitate interaction with protein partners and to serve as a marker for synaptic activity [35,38]. To determine whether the increase in locomotor activity seen after α-synuclein overexpression and the increased striatal tissue levels in these mice would be accompanied by altered α-synuclein serine-129 phosphorylation, we stained midbrain sections from AAV-DIO-hASYN WT injected DAT Cre mice with a phospho-serine-129 specific antibody at 21 and 90 days post virus infusion (Fig.…”

Alpha-synuclein aggregates are phosphatase resistant

“…PSER129 detection in the healthy mammalian brain (i.e., endogenous-PER129) has been inconsistent across studies [8,[15][16][17] with varying abundance, cellular localization, and regional distribution. We observed high variability in the steady-state level of endogenous-PSER129, which could be explained by either sample preparation or biological factors such as neuronal activity [5,6].…”